Cedar shake roofing in Washington, DC

Cedar is not common inside the District, but it shows up on houses that were designed around it. Shingle-style and Arts and Crafts homes in Takoma, Chevy Chase and Cleveland Park, a handful of cottages in Palisades and Spring Valley, and plenty of Capes and contemporaries in Bethesda, Potomac, McLean and Great Falls carry cedar shakes or sawn shingles.

Most were built with cedar on purpose. The wide, rough textures of hand-split shakes match stone chimneys, dark wood siding and steep gables in a way asphalt never quite does. When those roofs wear out, many owners want to keep the look.

In historic districts such as Takoma DC or Cleveland Park, keeping cedar where it was original makes historic review easier. Swapping to a different visible material goes through the Historic Preservation Office, and in Takoma Park MD the town's own historic district rules apply.

People use the words loosely, but they are different products. Shakes are split on at least one face, thicker and rougher, with deep shadow lines. Shingles are sawn on both faces, thinner and more uniform. Hand-split and resawn shakes give the classic rustic look, while taper-sawn shakes give a cleaner, more even surface.

Grade matters more than anything else. Number 1 grade, cut from 100 percent heartwood with edge grain, resists rot and splitting far better than lower grades that include sapwood and flat grain. We install only Number 1 blue label cedar shingles or premium grade shakes, and we can source pressure-treated cedar for a longer rated life on shaded lots.

Fire-retardant treated cedar is another option. It costs more, but some insurers and neighborhoods near wooded lots prefer it.

• Number 1 grade, 100 percent heartwood, edge grain
• Hand-split resawn shakes for a rustic texture
• Taper-sawn shakes or sawn shingles for a cleaner line
• Pressure-treated or fire-retardant options where needed

Wood roofs fail when they stay wet. On the humid DC summers and long wet springs here, a cedar roof laid tight against solid sheathing never dries out from below. We install shakes over spaced sheathing or over a breathable mat underlayment that creates an air gap, so the underside of each piece dries after rain.

Shakes get a strip of felt interlayment between each course, which keeps wind-driven rain out of the gaps between pieces. Each shake gets two stainless steel ring-shank nails. Galvanized nails react with tannins in the cedar and stain or fail early, so stainless is not an upgrade for us; it's the standard.

Keyways, the gaps between neighboring shakes, are spaced at about 3/8 to 5/8 inch and offset from the course below. Valleys get open copper or stainless metal wide enough to carry leaves, and chimneys get copper step flashing worked course by course.

Metal does most of the waterproofing on a cedar roof, so the metal has to last as long as the wood. We use 16-ounce copper for valleys, step flashing and chimney counterflashing, or stainless steel where budget is tight. Galvanized steel reacts with cedar tannins and rusts through well before the shakes are done.

Valleys on shake roofs are left open, with the metal exposed several inches on each side. Closed valleys trap leaves and needles, which hold water against the cut edges of the shakes and rot them in a few seasons. A center crimp in the valley metal keeps water from one slope from washing across to the other.

Chimneys and skylights need a cricket on the uphill side when they are wider than about 30 inches. Without it, leaves pile up behind the masonry and the shakes there rot first. We build the cricket from plywood, wrap it in ice barrier and cover it in copper so it sheds debris along with water.

Older cedar roofs in Chevy Chase and Bethesda often have skylights added decades after the roof was built, flashed with whatever was on hand. We replace those with proper step-flashed curbs during the reroof, since opening the area later means disturbing new shakes.

Many cedar roofs in Bethesda, McLean and Potomac sit under tall oaks and tulip poplars. Shade, leaves and summer humidity let moss, lichen and fungus grow, and debris piles up in keyways where it holds water against the wood.

Plan to clear debris every year, especially behind chimneys and in valleys. A copper or zinc strip at the ridge releases trace metals with each rain and slows moss on the slopes below. Trimming back limbs that hang over the roof helps more than any treatment.

Pressure washing cedar is a mistake. It strips wood fibers and shortens the roof's life. Soft washing with a cleaner rated for cedar, followed by a breathable preservative every few years, keeps the wood healthy. Our roof maintenance visits cover that cleaning and treatment schedule.

Some houses have outgrown cedar. Heavy shade from neighbors' trees you can't trim, a very low pitch, or an owner who doesn't want annual upkeep all argue for a different roof. Shakes need at least about 4 in 12 pitch to shed water well.

If you want the look without the work, designer asphalt shingles with a shake profile, synthetic shakes or standing seam metal are reasonable choices on houses outside historic districts. We price cedar alongside an alternative so you can compare the cost over the life of each roof.